A work-holding device having a clamping jaw with a multitude of clamping pins is known from Australian Patent No. 117,458. The clamping pins, which are circular in cross section and which are laterally encompassed by a frame, do not fill the frame completely. Several clearances exist in the neighbourhood of each clamping pin. When fixed to each other and to the frame by a lateral fixing force, the clamping pins show line shaped contact areas. With this arrangement, debris, which penetrates between the clamping pins, will be removed into the clearances between the clamping pins with applying the fixing force. Thus, the debris does not hinder the fixing of all of the clamping pins with regard to the frame by means of the fixing force, as long as it can be received by the clearances. The limited contact area of the clamping pins is uncritical for a sufficient non-positive connection of the clamping pins. On the contrary, elastic deformations of the clamping pins, which can occur when applying higher fixing forces, may support the fixing of the clamping pins with regard to the frame by way of a kind of positive connection. Additionally, the clamping pins with the circular cross section are easily manufacturable, for example by means of cutting-off to length appropriate bars of round bar steel. The fixing device of the known work-holding device applies the fixing force on a wall of the rectangular shaped frame, which, opposite to the other walls of the frame, is movable perpendicularly to the direction of main extension of the clamping pins. The fixing force is exerted by means of a fixing screw supported on the other walls of the frame. A clamping mechanism for applying a clamping force on the clamping jaw as a whole comprises a stationary but pivoted spindle passing through a tapped hole in the clamping jaw.
A work-holding device having a clamping jaw with a multitude of clamping pins is also known from U.S. Pat. No. 2,754,708. Here, the clamping pins are hexagonal in cross section. The clamping pins are packed up in the frame go that they fill up the frame completely, aside from the border region of the packing. Here also, the clamping pins are fixed with regard to each other and with regard to the frame by means of a movable wall of the frame, to which the fixing force is applied by a fixing screw. At their backsides, the clamping pins are connected with retaining bars, which pass through a through-drilled retaining plate and which are provided with a retaining collar behind the retaining plate. Helical compression springs are arranged on the retaining bars, which push the clamping pins away from the retaining plate forward to the workpiece. The clamping mechanism here also comprises a stationary but pivoted spindle passing through a tapped hole in the clamping jaw. During actual use of the work-holding device according to U.S. Pat. No. 2,754,708 it turns out, that the work-holding device reacts very sensitive to debris. In the case of penetration of any debris between the clamping pins, the lateral fixing force acts no more on all of the clamping pins, but it is borne by definite clamping pins only. The result is, that single clamping pins or total regions of clamping pins are not fixed with regard to the frame by means of the lateral fixing force.
The British Patent 595,803 discloses a holding device with two clamping jaws, which are horizontally divided into single clamping elements. Pressure chambers, to which oil pressure is admitted, are provided behind the clamping elements. The pressure in the pressure chambers pushes the single clamping elements forward and carries them. The pressure chambers of both clamping jaws known from the vice according to British Patent 595,803 are jointed together. A mobility of the whole clamping jaws against each other is not provided. Instead, pressure is applied on the communicating but principally closed pressure chambers for clamping a workpiece. However, no definite position of the workpiece clamped in the vice is achieved herein because in case of a displacement of the workpiece in clamping direction of the vice no rise of the pressure occurs as a reactio. One pressure chamber displaces exactly as much oil as it can flow after into the other pressure chamber. The same applies for twisting the workpiece in a plane, in which the single clamping elements of both clamping jaws are arranged side by side.
Work-holding devices for workpieces with a plurality of parallel and separately movable clamping elements are also known from German Patent 19 29 830 and German published Patent Applications 42 39 180 and 39 27 773.
U.S. Pat. No. 4,200,272 discloses a work holder for locating a workpiece of irregular shape during treatment. Said holder comprises a flat horizontal table and a two-dimensional array of vertically disposed spaced-apart rods mounted to be vertically movable in relation to said table and protruding upwards through said table. The table has upper and lower table surfaces through which said rods protrude upwards. There is a working clearance between each of said rods and each of said surfaces. Said first and second horizontal surfaces define therebetween a plenum chamber. Means are provided for admitting air under pressure to said chamber whereby to produce an upward flow of air through said clearances between each of said rods and said upper sable surface to prevent the ingress of debris from a workpiece supported by said rods. The rods are pushed upwards by means of helical springs arranged below said plenum chamber. A fixing mechanism is provided for fixing each rod to a frame of the table, separately.